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Public Information Statement
National Weather Service Taunton MA
905 AM EDT Tue Jul 18 2017
...Hurricane Preparedness Week in Southern New England...
...Rules of Thumb For Southern New England Hurricanes - Part 2...
The National Weather Service has declared this week as hurricane
preparedness week in southern New England. The following is the
second in a series of five statements, the first three with
rules of thumb for New England hurricanes and the last two with
preparedness actions.
Yesterday we discussed the fact that you should not concentrate
on when the eye is forecast to make landfall, since the
important impacts of the storm occur way out in advance of the
eye. Also any named tropical cyclone in the Bahamas should have
your attention.
The third rule of thumb is that you need to know where you are
with respect to the expected track of the eye in order to
determine your most likely hazards. Generally expect flooding
rainfall to the left of the track. To the right of the
track, damaging winds and storm surge inundation are the most
likely threats. This is not to say no other hazards will
exist, merely these are the most likely threats. It is
imperative you do not focus on the exact track as the impacts
will be felt many miles away from the track of the eye.
In the textbooks, hurricanes are perfectly symmetric. As the
tropical cyclone approaches, the rain and wind pound from one
direction, then the eye moves overhead and it is calm, then
the rain and wind pound equally as hard but from the opposite
direction. This scenario is true of storms at lower latitudes.
However, hurricanes that affect southern New England are
typically accelerating up the coast and becoming asymmetric.
This is because most of them are in the process of transitioning
from a purely tropical system to the structure almost like that
of a winter storm. As a result, flooding rains tend to occur to
the north and west of the track of the eye. Partial sunshine
occurs with only scattered showers to the south and east of the
eye. But that is where the powerful winds are, and where the
storm surge is maximized. After the eye moves through, most of
the rain is over. In terms of rain there is no second half. The
winds do shift directions and can be briefly strong on the back
side.
To illustrate this rule, take Hurricane Bob from August of 1991.
It tracked northeast across southeastern Massachusetts. Less than
one-half inch of rain occurred during the entire hurricane across
Cape Cod, to the right of the track. Six to seven inches of
flooding rainfall occurred over Foster/Glocester Rhode Island,
to the immediate left of the track. The strongest winds and
highest storm surge, however, occurred over Cape Cod and the
islands where gusts up to 125 mph occurred.
Irene in 2011 also exhibited this behavior, with devastating
rainfall to the left of the storm track across most of the East
Coast. The stronger winds were across Connecticut, Rhode
Island and portions southeast Massachusetts, which were to the
right of the track.
In 1955, Tropical Storm Diane took an unusual track. It
paralleled the south coast of New England, which put all of
southern New England on the rainy north and west side of the
storm. A foot of rain was common across a large portion of
interior southern New England, with the jackpot over Westfield
Massachusetts, where 18.15 inches of rain occurred in just 24
hours.
As with any rules of thumb, there can be exceptions, but they
are rather rare. One notable exception was Hurricane Carol in
1954 which had the heaviest rains just to the right of the track.
Stay tuned tomorrow for more rules of thumb for New England
hurricanes.
$$
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